The present invention relates to a small-size zoom lens, and more particularly to a zoom lens which is incorporated in handheld terminals and mobile phones and which has excellent portability by reduction of the overall length of the lens as well as to a digital camera and a portable information device using the same.
In recent years, handheld terminals called PDAs (Personal Digital Assistances), mobile phones and the like widely prevail, and most of them carry imaging devices such as digital cameras. These imaging devices use small-size CCDs (Charge Coupled Devices) and CMOS (Complementary Metal-Oxide Semiconductor) sensors to achieve downsizing. As these devices prevail, the imaging devices are required to be smaller as well as to achieve high definition and high performance, as a result of which zoom lenses are being mounted on thin casings such as mobile phones.
In such zoom lenses mounted on portable terminals such as mobile phones, a conventional zoom lens, in which a lens closest to the object side is driven, is not preferred in terms of dust control and impact resistance, but a zoom lens, which is structured so that only inner lenses of the zoom lens are driven while lenses closest to the object side and on the side of an image plane are fixed, has advantages for portable devices due to its sufficient robustness and easiness in dust control.
As such a zoom lens, for example, JP H11-249016 discloses a zoom lens composed of four negative, positive, positive, and positive components, the zoom lens having, in order from the object side, a first lens group having a negative refracting power, and a second lens group, a third lens group and a fourth lens group each having positive refracting power, in which only the second lens group and the third lens group are driven to perform variable magnification. In the zoom lens, an aperture stop is provided in between the first lens group and the second lens group, and lenses are glued together to form the fourth lens group, so that the zoom lens which is compact and smaller in number of lenses is achieved.
As an optical system of the same type, JP 3493406 discloses a zoom lens in which all the lens groups are structured from one lens by heavy use of aspherical surfaces.
However, in the structure disclosed in JP H11-249016,the fourth lens group, which is structured from two lenses, is close to the image plane so that its external diameter is large and its radius of curvature is small, which disables the thickness of the lenses from being reduced. Therefore, the fourth lens group structured from two lenses causes extreme increase in the overall length of the optical system. Moreover, as disclosed in JP 3493406, the respective lens groups structured from one lens make it difficult to correct chromatic aberration.